Electric Motors – The Basics

Electromagnetic force production is presented using a simple straight wire as a primitive form of electrical machine. Magnitude of force is quantified in terms of the magnetic flux density and current. Methods of enhancing flux density are investigated. Concepts of magnetic circuit, magnetomotive force (m.m.f.), and reluctance are introduced. Linear model is extended to rotary. Fundamental expressions for torque as a function of rotor volume are developed. Motion at constant speed – the important idea of ‘motional e.m.f.’ in the conductor – is discussed. Basic equations governing the electromechanical energy conversion process are given. Transient (run-up) behavior is examined. Finally, efficiency and thermal limits are explored.